Image Editing Basics

How to Resize Images

The size of a Photoshop image is measured in width and height, combined with a resolution value expressed as pixels or dots per inch (dpi). For example, you could have a 4x5–inch image at 300dpi. When resizing images, it is important to understand your minimum target resolution and to never go below it. (For example, in the print world, 300dpi is generally a target resolution.)

1. Open the Image in Photoshop

   Choose File, Open and select the image file with which you want to work.
   

2. Check the Image Size

   Choose Image, Image Size to open the Image Size dialog box. Make sure that the Constrain Proportions check box is enabled. This option ensures that the width-to-height ratios are maintained and prevents you from distorting the image as you resize it.
   

3. Deselect Resample Image

   Make sure that the Resample Image check box is disabled. Deselecting this option keeps you from accidentally degrading image quality, especially if you plan to enlarge the image. Resampling works well when you want to resize and shrink the image, but resampling can be disastrous when you're trying to increase the dimensions.
   

4. Enter Target Resolution

   Resolution refers to the number of dots per inch (dpi) or pixels per inch (ppi). For print, you want the image resolution to be between 225dpi and 300dpi; in contrast, the Web needs only 72dpi. Type the target resolution for this image in the Resolution field. As you do this, the dimensions (the Height and Width fields in the Document Size area) change, ensuring that image quality is not sacrificed. In this case, typing 300 in the Resolution field changed the dimensions from 14x21 to approximately 3x5.
   

5. Enter Target Dimensions

   Because resolution is tied to image dimension, changing the dimension values modifies the target resolution you entered in Step 4. To change dimensions without altering resolution, enable the Resample Image check box and select Bicubic as the interpolation method. If you are designing for the Web, enter the dimension size in the fields in the Pixel Dimensions area; if you are designing for print, use the Document Size section. Specify the units of measurement in the pop-up menus (remember that image quality degrades if you enable the Resample Image check box), and then increase the image dimensions. Enter the desired dimensions and click OK to resize the image.

How to Flip and Rotate an Image

You may have to reverse the orientation of an image for compositional or aesthetic reasons. This is relatively simple to do in Photoshop (provided that there is no text that would be reversed). In addition to reversing an image, you may want to rotate the entire image canvas, reorienting it to a new position. This is a common requirement for optimizing scans that were set up in the wrong direction. The main difference is that Free Transform operates on individual layers rather than the entire image (so your text, on a separate layer, won't be affected).

1. Open the File

   Choose File, Open and select the desired image file.
   

2. Rotate the Image

   Select Image, Rotate Canvas. From the submenu, choose 90° CW (clockwise), 90° CCW (counterclockwise), or 180°. In this example, I choose 90° CW. The command is executed as soon as you select it from the menu.
   

3. Apply Arbitrary Rotation

   Choose Image, Rotate Canvas, Arbitrary to open the Rotate Canvas dialog box. You can use this dialog box to specify the precise degree and direction of rotation. In this example, I want to rotate the image an additional 19° clockwise (CW). Click OK to rotate the canvas, which enlarges to accommodate the angled image.
   

4. Flip the Image Horizontally

   Choose Image, Rotate Canvas, Flip Canvas Horizontal to flip the image horizontally.
   

5. Flip the Image Vertically

   Choose Image, Rotate Canvas, Flip Canvas Vertical to flip the image vertically.
   

6. Observe the Results

   As you can see, rotating and flipping an image can greatly affect how the image is perceived. Although you haven't really changed anything about the image other than the way it is presented to the viewer, you can see that presentation is important.